It has been reported that up to 1.2 million Americans rely on wheelchairs for mobility, and this number continues to increase. Despite the high incidence of upper extremity (UE) musculoskeletal problems among individuals relying on wheelchairs, little published data exists regarding the biomechanics of wheelchair propulsion; particularly limited is the data addressing the relationship between UE loads and the increased risk of musculoskeletal problems. The investigators have developed a method for field analysis of the three-dimensional kinematics and kinetics of wheelchair propulsion at the shoulder, elbow, and wrist. The maximum moments, the joint positions corresponding to the maximum moments (Jp max), range of motion (ROM) arcs, for 14 selected UE joint functions will be determined for 45 wheelchair users in the proposed project. The maximum moment for each joint function in wheelchair propulsion will be expressed in terms of a wheelchair propulsion strength rating (WPSR). The WPSR is being defined as the ratio between an intersegmental joint moment generated during propulsion to that generated during an isometric maximum strength test of that joint function. Specific Aim 1: To compare maximum loads for different joint functions in wheelchair propulsion. It is hypothesized that there is a difference in the WPSRs between upper extremity joint functions in wheelchair propulsion for a given ramp grade and a given propulsion technique. Specific Aim 2: To compare two different wheelchair propulsion techniques, pull-push and pumping, by comparing WPSRs, JP max S, and ROM arcs for the two propulsion techniques. It is hypothesized that the WPSRs, ROM arcs, and JP max S are different for the two propulsion techniques. Specific Aim 3: To determine the effects of ramp grades on the WPSRs, Jp max S, and ROM arcs. It is hypothesized that the WPSRs, JP max S, and ROM arcs are functions of the ramp grade. Contributions from this study will ultimately help improve wheelchair and environmental design, so that improved efficiency and reduced risk of chronic injury allow the individual wheelchair user to remain as independent and active as possible in society.